The invention concerns a loudspeaker box having a housing and at least one loudspeaker with a chassis.
Loudspeakers are normally built with their chassis in a housing (i.e. a so-called enclosed loudspeaker), in order to avoid, to the greatest possible extent, an acoustical short circuit, i.e. an interaction between the sound generated by the rear side and front side of the speaker and the associated cancellation of those sounds. The sound cancellation results from the motion of the loudspeaker""s membrane and the resulting combination of the two out of phase sound waves generated by the membrane""s motion. The resulting sound propagation pattern of closed loudspeakers is uniform in nearly all directions, especially for low frequencies. For higher frequencies a directionality will be produced, because of the increase in reflections and propagation time effects caused by the decrease in wavelength, whereby the sound propagation will be concentrated in a particular direction.
The sound cancellation pattern of an open loudspeaker (i.e. a loudspeaker without a housing) is limited, in contrast, by frequency dependency whereby a good sound cancellation pattern is achieved to the greatest possible extent for low frequencies and for high frequencies a substantially poorer sound cancellation pattern is achieved. Additionally, in the region of the surface of the loudspeaker""s membrane, a good sound cancellation (i.e. null points) pattern arises over a particularly large frequency band. As a result, the open loudspeaker usually demonstrates a so-called dipole-curve sound pattern in the region of the loudspeaker (also called an xe2x80x9ceight-characteristicxe2x80x9d curve).
A disadvantage of both loudspeakersxe2x80x94open and closedxe2x80x94is that a sound playback with adequately good directivity in the bass region is not assured. For high frequencies, the closed loudspeaker (the loudspeaker box) is especially suitable, since it achieves an especially good directivity. In the bass frequency region, neither the loudspeaker box nor the open loudspeaker exhibit an adequately good directivity.
Hence, to produce a good directivity in the bass frequency region, usually multiple loudspeakers, e.g. two loudspeakers, will be coupled together. In that case, both of the loudspeakers work in opposing phase from one another. The coupling of both loudspeakers is performed in such a way that the resulting acoustical and electrical paths are adjusted to one another so that the electrical propagation time approximately matches the acoustical propagation time. Different directivity characteristics, e.g. kidney shaped or clubbed shaped directivity characteristics, are realized depending upon the type of loudspeaker that is utilizedxe2x80x94a closed or open loudspeaker. Alternatives that can also be used to attain directivity in the bass region are called loudspeaker arrays or loudspeaker lines. These solutions all require additional loudspeakers and therefore their construction is especially equipment intensive and expensive.
The invention is based upon the task of providing a loudspeaker box that achieves a directionality, including in the bass region, in a particularly simple way. In addition, a headrest shall be provided that realizes a good bass playback response.
The first stated problem is inventively solved by a loudspeaker box that has a housing and at least one loudspeaker with a chassis, that is surrounded in such a way by a housing wall so that in the low frequency region the sound on the rear side and on the front side of the loudspeakers superimpose themselves with an amplification in sound in a given direction.
The invention starts with the concept, that for the individualized broadcasting of sound into predetermined spatial areas, taking into consideration sound propagation, a directionality is to be achieved over a large frequency range, wherein loudspeaker feedback should be avoided. The loudspeaker construction should also be compact, so that it is also useful for small loudspeaker boxes. In place of the traditional loudspeaker arrangement comprising several loudspeakers to achieve a response in the bass region, the invention starts with a single loudspeaker that has an associated chassis and arranges those elements on the housing wall in such a way that a sound amplification arises in a given direction through the superposition of portions of the produced sound. Thereby the housing wall operates as a flat sound-wall for the loudspeaker, so that the combined effect of the rest of the housing front-side and rear-side sounds, which are of different power and phase, leads to a directivity with a sound amplification in a preferred direction and with a sound reduction in the opposite direction. In other words: a directivity in the low frequency region will also be beneficially achieved for the single loudspeaker through the arrangement of the single loudspeaker in the specially adapted housing. Consequently, the directivity of the delivered output in the low frequency region will particularly advantageously be increased.
The sound from the rear side and the front side effectively superimpose themselves in the shape of a pear in the area of the loudspeaker. Such a pear-shape directivity (also called a hyper kidney) is preferably employed in the near field of the loudspeakers and in the bass frequency region. Equally good is, for example, a kidney-form directivity characteristic. Through the appropriate design of the housing wall a directivity can be adjusted such that therefrom a particularly high directivity in the near field of the loudspeaker results for a specified distance.
Preferably the chassis is arranged as a symmetrical, mirror image of the housing. This symmetrical arrangement of the chassis in the cross-section or longitudinal section of the housing results in both sidesxe2x80x94front and a rear sidesxe2x80x94each having an approximately equal volume of air. Therefore the air resistance or stiffness exerted upon the movement of the speaker""s membrane is approximately equal in both directions of movement. Moreover the approximately equal volumes of air on both sides cause an especially equalized base frequency response.
The housing is suitably constructed in the form of a cylinder. Such a tube shaped housing with a circular cross-section makes particularly possible a simple symmetrical arrangement of the chassis. Additionally, a housing in the form of a rectangular box is also preferably suitable for the construction of the loudspeaker box. The cross section of the rectangular box is, for example, a rectangle or a square. Furthermore, a housing may be built with an elongated cross section or longitudinal section, preferably an oval chassis.
A sound opening is preferably provided in the housing for at least both the front side and rear side sound. An equal number of sound openings on both sides is preferred. Furthermore the shape of the sound openings is appropriately selected for particularly good directivity. Advisably at least one of the sound openings is located in the area of the sound cone of the rear side and front side sounds.
In order to obtain sound directing acoustic dampening, at least one of the sound openings is provided with dampening material. For example, the sound opening on the rear of the chassis is provided with dampening material. A selective sound reduction will be produced on one side through this covering of the rear side sound opening. For example, one side of the frequency response will be lowered in broadband, for example, attenuated 1 to 8 dB. A pear shaped sound propagation pattern is obtained through this single sided selective sound dampening. Fibrous material is an example of material that may serve as a dampening material. The sound reduction can be adjustable or variable by installing different acoustical dampening material or variable quantities or thickness of the dampening material, so that an especially good directivity is achieved at a given distance from the loudspeaker box.
This is suitable for the use in a vehicle, in particular in a headrest, in part through the especially compact design and the especially compact construction of the loudspeaker box. Depending on the type and extent of the sound-filled areaxe2x80x94the area of the seat associated with the headrest, for example xe2x80x94and also depending upon the desired intensity of the sound of this area, at least one loudspeaker box is integrated into the headrest. Beyond that additional loudspeaker boxes can be provided, particularly in the seat or seat back. The stability of the loudspeaker box also contributes to the mechanical stability of the headrest, particularly when it is part of the frame of the headrest. The mechanical stability of the headrest is provided by an appropriate frame construction and the housing of the loudspeaker box is also so constructed, for instance, out of a soft synthetic material. The opposite case is a loudspeaker box housing that is preferably built out of hard synthetic material or aluminum, where the housing itself contributes to the stability of the headrest. This hard housing section will be appropriately padded, for example, with foam.
The advantage obtained through the invention particularly lies in a housing comprising a housing wall surrounding the loudspeaker chassis and wherein the structure of the sounds from the front side and the rear side of the loudspeaker affect each other, especially at low frequencies, and wherein the sound of one side is specifically so lowered, so that the two sound parts, which each have different power and phase, lead to a superposition with a directivity that has a sound increase or amplification in a preferred direction and a sound reduction or attenuation in the opposite direction.